1. Field of the Invention
This invention relates to an electronic musical instrument. More particularly, the invention relates to a synthesizer type electronic musical instrument which comprises a plurality of operation units (operators) which perform waveform generation and frequency modulation thereof.
2. Prior Art
An electronic musical instrument and a method of the type are disclosed in U.S. Pat. No. 4,554,857 and U.S. Pat. No. 4,249,447.
First, the instrument disclosed in U.S. Pat. No. 4,554,857 has a plurality of operators (six, for example) to generate a number of waves and perform the modulation thereof. The operator includes a wave generator that contains a sine wave table having sine wave data, a phase generator that generates phase data that designates the address of the sine wave table, and an amplitude-envelope generator that modulates output data from the sine wave table. The phase generator generates the phase data on the basis of frequency-number data that indicates the frequency of a depressed key, and the wave generator then generates a waveform corresponding to the phase data. The wave generator has as one of its functions to modulate phase data by use of external data and/or output data of other operators, so that the phase data has complex variations over time, and hence the operator can produce a rich, dynamic sound. These operators are arranged in a number of different configurations called algorithms. In FIG. 5 of the above U.S. Pat., thirty-one algorithms A-1 to A-31 are shown. Depending on its location in an algorithm, an operator will function either as a modulator or a carrier generator, producing a broad range of tones. A performer selects, before performance, one of these algorithms to obtain the tones he desires.
Second, the U.S. Pat. No. 4,249,447 discloses a method for generating waves having a desired harmonic structure by means of an operator that has a feedback loop. The desired harmonic structure can be obtained by varying feedback parameter .beta..
The instrument or method mentioned above is an effective and powerful one. However, there are still some problems to be solved, as follows:
(a) Although the phase data produced from each phase generator can be modulated independently, the frequency-number data applied to the phase generator is common to all the operators. In other words, pitch data (i.e., frequency-number data) applied to each phase generator is the same data. This imposes limits on creating wide-ranging and complex tones.
(b) Conventionally, feedback parameter .beta. of the operator is kept constant during a performance, that is, it must be set before a performance and cannot be varied during the performance. Setting the feedback parameter .beta., or an algorithm of the operators before performance makes it possible to produce a wide range of tone colors. However, this also imposes certain limits on achieving expressive performance. This is because key touch cannot effect variation of feedback parameter .beta., and hence, it is not possible to obtain a drastically changing, dynamic tone with variation of touch.
(c) A conventional pitch-envelope generator produces an envelope defined by a predetermined rate and level of data. Consequently, an envelope pattern is kept constant as long as the tone is not changed. In a real musical instrument (particularly in wind instruments), however, delicate pitch variance occurs in every note because of fine changes in expiration and lip movement. The conventional instrument or method cannot simulate the delicate undetermined pitch variance.
(d) The frequency-number table is used to correlate a keycode and frequency-number data that determines the pitch of a key. A certain conventional instrument is provided with a tuning editor that rewrites contents of a frequency-number table so that an arbitrary frequency number is assigned to a desired key. Hence arbitrary pitch can be assigned to a desired key. The assignment of pitch data to each key, however, is very tedious and is time consuming.